1. Field of the Invention
This invention relates to an improved method of removing heat-insulating material from an ingot mold prior to the removal of the ingot from the mold.
2. Description of the Prior Art
In steel making, there are a variety of ingot molds used for forming steel ingots. There are also a variety of methods used to counteract the contraction cavities which form during solidification of the ingot. The more common methods of counteracting the contraction cavities which form during solidification of the ingot entail the use of heat-retaining means, commonly referred to as "hot tops," alone or in conjunction with heat-insulating material. Examples of the various uses of hot tops and insulating material are depicted in Vallak U.S. Pat. No. 3,766,965.
Vallak teaches the use of permanent hot tops as an improvement over previous hot tops which were consumed or destroyed during solidification of the ingot. These previous consumable hot tops, which are still frequently used in steel production, are generally formed of heat-insulating and/or exothermic material held into the form by a bonding agent. On being exposed to the high temperatures associated with solidifying ingots, the bonding agent is destroyed leaving the heat-insulating material on top of the ingot. This material, which may consist of silica, asbestos, iron oxide and/or aluminum powder, is usually frangibly caked and must be removed prior to, or at the time of, removing the ingot from the mold.
The heat-insulating material in powder form, which is used in conjunction with consumable or permanent hot tops, is generally also composed of silica, asbestos, iron oxide and/or aluminum powder. This powdered insulating material, which is usually frangibly caked by the heat from the solidifying ingot, must also be removed prior to, or at the time of, removing the ingot from the mold.
The common methods of removing the caked insulating material result in wide dispersion of the material in the ingot stripping shop. One method, for example, is to invert the mold and permit the caked material to fall to the floor where it breaks apart into smaller caked pieces and releases a large amount of dust. Besides the inconvenience and hazard present due to the quantity of insulating material at temperatures of up to 800.degree. C spread on the floor of the shop, the dispersion of great amounts of dust in the shop creates a severe health hazard to the shop personnel.
Airborne dust is responsible for the many serious disabling diseases, and the inhalation of any dust should be avoided. Some dusts, by virtue of their composition and particle size, are, however, particularly dangerous; relatively small concentrations in the atmosphere can, over the years, lead insidiously to serious and permanent damage to the lungs. It is unfortunate that both silica and asbestos, with their attractive thermal characteristics, are among the most dangerous sources of respirable dust.
There have been few attempts to reduce the disadvantages and hazards of the presently common methods of removing ingots from ingot molds. One such attempt is taught in Gathmann U.S. Pat. No. 1,719,542. While that patent teaches the use of suction to remove insulating material from the top of flat ingot molds in order to prevent its dispersion throughout the ingot-stripping shop, it has numerous disadvantages. The invention taught in Gathmann is a large, cumbersome, stationary machine requiring a great deal of power and requiring that the ingot molds be taken to the machine.
The primary difficulty with the invention in Gathmann is that the insulating material commonly used today is the type which cakes on being exposed to the heat of the solidifying ingot. Gathmann is intended to be used with insulating material that retains its powder composition so that it can be easily removed from the ingot mold by suction. In order for the invention in Gathmann to remove a caked layer of insulating material, a great deal of vacuum suction would have to be provided to break up and remove the caked material. In addition to the extreme inefficiency of the Gathmann method of removing caked insulating material, Gathmann does not provide a means for removing the insulating material which is located around the sides of the shrunken, solidified ingot within the mold and in the corners and recesses in the top of the mold before the removal of the ingot.
It is the disadvantages and hazards of the methods used to remove ingots from ingot molds, whether that of Gathmann or the other commonly used methods, that the instant invention is intended to ameliorate.
Other vacuum systems are known in the prior art. An example of such a system is taught in McClure U.S. Pat. No. 3,535,730. The prior art vacuum systems, however, are not designed nor intended for use with high temperature materials such as insulating material from ingot molds at temperatures up to 800.degree. C. Further, the ends of the low-pressure conduits in the prior art systems are designed for removing loose particulate material and are not for use in reducing caked material to sizes less than the diameter of the orifice.